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Full text of "Treatise On Applied Analytical Chemistry(Vol-1)"

452

STEARINE  (STEARIC ACID)

In general stearine forms hard, opaque, white masses, somewhat greasy
to the feel and soluble in alcohol, especially in the hot.

Analysis of commercial stearines comprises principally the following :

1.  Solidifying Point (Titer) .—This is determined by Dalican's method
(see p. 418), the content of stearine being deduced by means of the corre-
sponding table ;   when, however, fatty acids alone are   concerned, the

number given in the table is multiplied by — (see p. 419).

«/•-'

2.  Acid, Saponification and Iodine Numbers.—By the methods
given in the preceding chapter.

The iodine number depends on the quantity of oleic acid (and maybe
of iso-oleic acid) in the stearine and this may be calculated from the iodine
number by means of the formula

0 = — x I, or 0 = i-ii x I,
90,

where 0 = oleic acid sought   I = iodine number of the stearine and 90
is the iodine number of pure oleic acid.

3.  Detection   of   Various   Extraneous   Substances.—Commercial
steariftes sometimes contain solid paraffin or ceresine, wool fat stearine, wax
and carnauba wax.   The presence of such substances may be suspected as
a rule when the acid number of the stearine is less than 195, but may be
proved definitely as follows :

(a)  A. few grams of the stearine are digested in the hot with 95% alcohol.
If the substance does not dissolve completely, the liquid is allowed to cool
and filtered and an examination made of the insoluble part.    The latter
may contain solid paraffin or ceresine, beeswax or carnauba wax, their
presence being indicated by the melting point, the acid and saponification
numbers, etc. (see articles on Paraffin Wax, Ceresine and Beeswax).1

(b)  A quantity of the stearine is hydrolysed with alcoholic potash and the
unsaponifiable substances extracted and examined by the methods indicated
on p. 388 et seq. ; the presence of cholesterol will indicate the presence of
wool fat stearine in the substance.

If then it is necessary to determine the various acids composing a stearine
(stearic, palmitic, oleic) and to test for stearolactone, the methods indicated
in the preceding chapter (see pp. 384 and 383) may be followed.

Finally, when the presence of lactones is excluded, that of neutral fat
may be deduced from the ester number and may be confirmed by testing
for glycerine (see p. 384).

Commercial stearines usually solidify between 48 and 55° (liter), the value
for saponification stearine being somewhat higher than that for distillation
stearine.

The acid number should "not be less than 195 : if it is less than this, the
presence of neutral fats or extraneous substances is denoted.

1 The presence of carnauba wax may be recognised also from the fact that, besides
lowering the acid and saponification numbers of the stearine, it raises the melting
point considerably, 5% of carnauba wax being sufficient to raise the melting point
of a stearine by 10°, fat.